1. Field of the Invention
This invention relates generally to cooling agents or compositions that can be used to cool surfaces, liquids and solids when activated upon mixing with water and more particularly to cooling agents that are effective, resistant to combustion, insensitive to detonation, non-toxic and recyclable as a balanced NPK fertilizer.
2. Description of the Art
The present invention relates to compositions which produce an endothermic reaction when mixed with water, and which are non-toxic, non-explosive and can be recycled as a balanced NPK fertilizer when no longer useful as a cooling agent. Although not so limited, the invention has particular utility when used as a cooling agent in therapeutic cold packs for the treatment of sprains and injuries; for chilling of beverages and packaged foods; and for other applications where it is desirable to cool surfaces, fluids or objects.
Compositions producing an endothermic effect and devices or containers that utilize such compositions are known in the prior art. Such compositions typically produce their endothermic effect by either chemical reaction or by heat absorbing processes. Examples of endothermic chemical reactions include: the reaction of barium hydroxide octahydrate crystals with dry ammonium chloride with the subsequent evolution of ammonia; the reaction of thionyl chloride with cobalt(II) sulfate heptahydrate; and the reaction of ethanoic acid with sodium carbonate. Examples of such endothermic processes include: melting ice cubes, melting solid salts, evaporating liquid water, making an anhydrous salt from a hydrate and the dissolution of salts in water.
As a general rule, compositions that undergo endothermic reactions are useful for cooling but often utilize toxic reactants such as cobalt and barium hydroxide or produce noxious and irritating byproducts such as ammonia, or gasses that are difficult to contain and process such as carbon dioxide. Heat-absorbing processes are thus more commonly used to cool substances compared to chemical reactions. With respect to cold packs and beverage coolers, heat-absorbing processes based upon the dissolution of various salts in water are commonly described. Here the selection of a particular material has primarily been based upon the magnitude of its positive enthalpy of solution (heat of solution) and its solubility in water or another solvent whereby the most effective compositions have the highest positive heat of solution and highest solubility.
With respect to the above, U.S. Pat. No. 1,894,775 disclosed the use of various sodium, potassium and ammonium salt solutions, including sodium acetate, ammonium nitrate and sodium thiosulfate mixed with water, to provide therapeutic cooling in 1933. Subsequently many other patents have disclosed the use of additional compounds along with various wetting and gelling agents and co-solvents other than water to improve the cooling performance of endothermic compositions when applied to cold packs and beverages. As an example, U.S. Pat. No. 3,957,472 describes a chemical heat transfer unit that uses compounds selected from a group that includes ammonium sulfamate, potassium nitrate, ammonium bisulfate, ammonium bromide, ammonium bicarbonate, ammonium iodide, ammonium magnesium selenate, ammonium maganese sulfate, ammonium phosphate dibasic, ammonium potassium tartrate, ammonium salicylate, ammonium sulfate, ammonium sodium sulfate, ammonium thiocyonate, ammonium persulfate, potassium phosphate, potassium sulfate, potassium sodium tartrate, potassium thiocyanate, potassium iodide, potassium chloride, urea, afenil, sodium acetate, sodium citrate, sodium nitrate, sodium thiocyanate, sodium thiosulfate, citric acid, tartaric acid, ferric ammonium sulfate and thiourea. In another example, U.S. Pat. No. 4,081,256 describes an endothermic composition and cold pack whereby urea, hydrated sodium acetate, potassium chloride, potassium nitrate, ammonium chloride, and guar gum are blended together to extend the cooling life of the cold pack. In still other examples, U.S. Pat. No. 4,010,620 utilizes ammonium chloride and ammonium nitrate for maximum cooling effect; U.S. Pat. No. 6,233,945 describes an extended life cold pack that uses ammonium nitrate, ammonium sulfamate, ammonium nitrite, ammonium iodide, ammonium bromide, sodium chloride, sodium nitrate, sodium nitrite, sodium carbonate, sodium bicarbonate, potassium nitrate, potassium nitrite, urea, methylurea, and combinations thereof; U.S. Pat. No. 5,429,762 discloses a cooling agent consisting of one or more of a group comprised of disodium hydrogen phosphate, sodium dihydrogen phosphate, trisodium phosphate, sodium ammonium hydrogen phosphate, diammonium hydrogen phosphate, and hydrates thereof; and U.S. Pat. No. 4,010,620 describes a cooling system that utilizes sodium nitrate, ammonium nitrate, ammonium thiocyanate, potassium thiocyanate, and ammonium nitrate individually or in combination.
A review of the prior art reveals that, although a wide variety of chemical compositions have been disclosed, only a select few are preferred based upon performance as a cooling agent. This is best illustrated by a review of the selected endothermic compounds shown in Table 1.
TABLE 1SELECTED ENDOTHERMIC COMPOUNDS USEFUL FOR COOLING SURFACES, SOLIDS AND LIQUIDSPredicted FinalSolubilityHeat AbsorbedTheoreticalPredicted ChangeTemperature of 255 gmLD50(gm solute(during dissolutionChange inin Temperature ofof liquid exposed to(oral-Heat ofper 100 gmof compound inTemperaturea saturated solutionsaturated solutionMWrat;Solutionwater at100 gm of water atof a saturatedexhibiting 30% heatexhibiting 50% heatSolute(gm/mol)mg/kg)(kJ/mol)20° C.)25° C. in kJ)solution (° C.)loss (° C.)loss (° C.)C12H22O11342.3297005.4201.93.193224C6H12O6180.162580011492.995324C6H12O6•H2O198.162580019494.708523CO(NH2)260.0784711510826.97312216KF•2(H2O)94.132456.9734925.84141017KCl74.55260017.2234.27.90141022KClO3122.55187041.387.32.465424KClO4138.5410051.041.50.551125KBr119307019.8765.310.90161121KBrO310632141.136.912.686424KI166186220.3314017.15171219KIO321413627.744.740.611125KNO285.1125013.3530648.00282017KNO3101.1375034.8931.610.91201421K2S2O3•5H2O360.328024720526.74211516KCN65.12511.7271.612.89181321KCNO81.1284120.257518.72261819KCNS97.1885424.2322455.8541297KMnO4158.04109043.566.31.744324K2SO4174.25660023.811.11.523225NaF41.99520.914.130.090025NaCl58.4430003.8835923.8412917NaClO290.441650.33390.140025NaClO2•3H2O144.4416528.58397.7213922NaClO3106.44120021.7210120.61251718NaClO4122.44210013.8820122.79181318NaClO2•H2O140.44210022.5120132.22261814NaBr•2H2O138.89350018.6490.512.15151121NaBrO3150.8930126.937.46.6712823NaI•2H2O185.89434016.1318415.9713920NaIO3197.8918020.299.470.972125NaNO26818013.8980.816.50221520NaNO384.99323620.587.621.13271918NaC2H3O2•3H2O136.08353019.668512.28161121Na2S2O3•5H2O248.17230047.47915.09201420NaCN4961.21581.432225NaCN•2H2O85618.588217.92241619NaCNO65.01519.211032.49372614NaCNS81.057646.8313911.7112821Na3PO4163.94740015.98.80.852125NaHCO383.99422016.77.81.553224NH4Cl53.49165014.7829.78.21151122NH4ClO4117.4910033.4720.85.9312823NH4Br97.94270016.7878.313.42181321NH4I144.947613.7217216.28141020NH4IO3192.9450031.818230.00251815NH4NO264.045719.2515045.09433010NH4NO380.06221725.6915048.1346329NH4CN44.0652517.576023.93362517NH4CNS76.1295422.5814442.72422911(NH4)3PO4149300014.4537.73.666424CH3NH3Cl67.5216005.7730.62.615324AgClO4207.32Toxic7.3855719.837518AgNO2153.87Toxic36.944.21.012225AgNO3169.87Toxic22.5925734.18231614RbClO4184.92331056.741.30.401125RbNO3147.47462536.4844.2810.95181321CsClO4232.36331055.441.970.471125CsNO3194.911200409.161.884324BaCl2•2H2O244.2711820.58312.615324MgSO4•7H2O246.36284016.1125516.6711820
In Table 1, the selected endothermic compounds (solutes) are classified with respect to their toxicity, heat of solution and solubility in water. Toxicity is measured by the oral rat LD50 value for a compound taken from various toxicological databases or from the Material Safety Data Sheet (MSDS) for the compound or from other indicators of toxicity if LD50 data isn't available. Compounds with an LD50 above 1000 are preferred for applications where there is a potential for human and environmental exposure. Heat of solution values are taken from CRC Handbook of Chemistry and Physics, 90th Ed. Solubility values are taken from the Solubility Database shown on the International Union of Pure and Applied Chemistry/National Institute of Standards and Technology website.
An endothermic process absorbs heat from the environment during the dissolution of the compound in water. The theoretical heat absorbed during the dissolution of compound in 100 gm of water at 25° C. in kJ can be calculated from the following equations using the data in the table:[HSol]*[moles of solute]=[mass of solution]*Cp*[T1−T2]  1.                where HSol is in kJ/Mol        mass of solution refers to the mass of a saturated solution in 100 gm of water        Cp is assumed to be 4.184 J/g ° C.        T1 is 20° C.        T2 is the final temperature of the saturated solutionΔq=heat absorbed=[mass of solution]*4.184*[T1−T2]  2.        
The theoretical heat absorbed and the final theoretical temperature of the saturated endothermic solutions are shown in the table.
This data was then used to predict the cooling effect of saturated solutions of the various endothermic compounds upon a typical beverage container having a volume of around 12 ounces. For a reference, approximately 60 grams of 200 mesh ammonium nitrate was thoroughly mixed with approximately 50 grams of water in an un-insulated 100 ml sealed container which was then placed in a larger sealed un-insulated container having a volume of around 360 ml that contained around 255 ml of water. The larger sealed container had approximately the same dimensions and surface area as a typical 12 ounce beverage can. After around 30 seconds, the temperature of the saturated solution in the 100 ml container attained −7° C. from an initial temperature of 25° C. and after around 3 minutes the temperature of the water in the 360 ml container attained around 9° C. from an initial temperature of 25° C. This reference test indicated that the theoretical change in temperature of a saturated solution of ammonium nitrate was approximately 30% more than the measured change in temperature due to heat losses from the 100 ml container while the container was being mixed prior to placing it in the 360 ml container that contained the water. A similar calculation showed that heat losses from the un-insulated 360 ml container was around 50%. The heat loss factors were then used to determine the predicted temperature changes shown in the table for the various saturated salt solutions and for a 360 ml container filled with 255 ml of liquid exposed to the various saturated salt solutions. The predicted results were then used to rate the performance of the selected endothermic compounds in terms of their performance as a cooling agent.
The compounds predicted in the table to be most useful as cooling agents should show at least a 10° C. reduction in temperature when dissolved in water and include urea (CO(NH2)2), potassium fluoride dihydrate (KF.2(H2O), potassium chloride (KCl), potassium bromide (KBr), potassium iodide (KI), potassium nitrite (KNO2), potassium nitrate (KNO3), potassium thiosulfate pentahydrate (K2S2O3.5H2O), potassium cyanide (KCN), potassium cyanate (KCNO), potassium thiocyanide (KCNS), sodium perchlorite (NaClO3), sodium perchlorate (NaClO3), sodium perchlorite dihydrate (NaClO2.H2O), sodium bromide dihydrate (NaBr.2H2O), sodium nitrite (NaNO2), sodium nitrate (NaNO3), sodium acetate trihydrate (NaC2H3O2.3H2O), sodium thiosulfate pentahydrate (Na2S2O3.5H2O), sodium cyanide dihydrate (NaCN.2H2O), sodium cyanate (NaCNO), ammonium chloride (NH4Cl), ammonium bromide (NH4Br), ammonium iodide (NH4I), ammonium iodate (NH4IO3), ammonium nitrite (NH4NO2), ammonium nitrate (NH4NO3), ammonium cyanide (NH4CN), ammonium thiocyanide (NH4CNS), silver nitrate (AgNO3) and rubidium nitrate (RbNO3).
Of this group, potassium fluoride dehydrate, potassium nitrite, potassium thiosulfate pentahydrate, potassium cyanide, potassium cyanate, potassium thiocyanide, sodium nitrite, sodium cyanide dihydrate, sodium cyanate, ammonium iodide, ammonium iodate, ammonium nitrite, ammonium cyanide, ammonium thiocyanide, and silver nitrate have LD50 values below 1000 or are toxic and are less than desirable for use in a consumer-oriented product such as a cold pack or beverage coolant. Potassium nitrite, potassium nitrate, sodium perchlorite, sodium perchlorate, sodium perchlorite dihydrate, sodium nitrite, sodium nitrate, ammonium nitrite and ammonium nitrate are all strong oxidizing agents and thus are reactive and have a tendency to promote combustion or are unstable during storage. Urea is also described as being unstable when mixed or blended with a wide variety of other endothermic compounds including ammonium nitrate, and blends of urea and other compounds that are described in the prior art as having synergistic coolant properties are rendered ineffective by a reduced shelf-life. Potassium nitrite, potassium nitrate, sodium nitrate, ammonium nitrite and ammonium nitrate are also capable of detonation and explosion, with ammonium nitrate having a particularly bad reputation as the explosive of choice for weapons of terror even though it is one of the most effective cooling agents disclosed in Table 1 and in the prior art. Mixtures of ammonium nitrate and urea are also commonly formulated together to make powerful commercial explosives.
Chemical cooling agents also suffer from the stigma of being a wasteful product that is not easily reused or recycled. Many of the endothermic compounds and compositions shown in Table 1 or disclosed in the prior art are classified as hazardous substances or are harmful to the environment if disposed in an improper or imprudent manner after they no longer have utility as a cooling agent.
For all of the above reasons, cooling agents and compositions described in the prior art have had limited commercial success with the possible exception of cold pack applications. The most effective commercialized cold pack applications, however, utilize ammonium nitrate or mixtures of ammonium nitrate and urea and are susceptible to increased regulation and subject to restrictions on use, and may not be available for use in consumer products in the future.